Todd Markle

Todd is a friend of Ethan, and one of the first people we see bullying Robin. He spurs Carson to bully Robin by taking her sketchbook.

Personality
Todd seems very eager to go out of his way to harass someone, even going out of his way to step on a piece of paper Robin was picking up, while feigning innocence. He's a very active member in Ethan's friend group, in regards to bullying Robin.

Ethan
Todd and Ethan are friends, but not much is known in regards to their relationship outside of being scolded by Ethan.

Jack
Todd and Jack are thought to be friends, but are not often seen interacting

Carson
He is seen to encourage Carson in his efforts to bully Robin.

Robin
It's not known why, but Todd goes out of his way to bully and harass Robin, along with Carson.

Trivia

 * He is a right fieldsman for The Carmikal Talons, their school baseball team.